A technique to analyze Particle Image Velocimetry (PIV) images with strong refractive distortion is presented. Based on a muti-level optical flow algorithm, the approach has been benchmarked with synthetically generated PIV images, and has been successfully applied to both experimental PIV and Laser Induced Fluorescence (LIF) images. To improve velocity field estimation, new symmetric spline and advection warping methods are proposed together with a data-driven method to impose boundary conditions. To address a historical weakness of optical flow PIV methods, a framework is presented to select the smoothness parameter for experimental images. An analysis of an experimental image series with severe blurring and intensity distortions demonstrates the viability of the techniqueShow more